The present invention relates to multiple video monitoring--that is, to the simultaneous monitoring of pictures received from a plurality of video picture sources--and is particularly concerned with such monitoring for security and similar surveillance purposes.
The use of video cameras and their associated video monitoring units has become an indispensable component of modern security and protection services. The number of cameras that might be employed at an institution has steadily increased with time as the expense of surveillance cameras has decreased. In some locations, such as gambling casinos, it is not uncommon for hundreds of cameras and their associated monitors to be in use.
In any such system, a compromise has to be struck between cost and effectiveness. For maximum effectiveness, the picture from each separate camera would be watched by a separate security officer. However, that would normally involve grossly excessive wage costs, particularly in camera-rich and monitor-intensive settings. Each operator (security officer) is therefore assigned a plurality of pictures to watch. Such surveillance imposes a considerable strain on the operator, in that he or she must continually scan a number of individual television monitors equivalent to the number of video sources.
It should be noted that limitations may also be felt as a result of the physical size of the video monitors. Even if no expense were spared in the numbers of operators assigned to view monitors, it rapidly becomes prohibitive to install and maintain a large number of expensive and physically large monitor units in location where operating space is of a high value (such as a gambling casino).
Staying with the example of a gambling casino, the design of the details of such a system involves a choice between a number of further and partially conflicting requirements. With the operator being assigned to observe a set of monitors, the pictures should be large enough to allow the operator a good view of the details of each picture. This is normally achieved by placing the operator within easy view of several large monitors. This achieves the immediate object, but naturally results in the operator being left with one or more of the monitors outside their immediate gaze if their attention should be drawn to an activity on a single monitor.
One apparent solution is to concentrate a number of smaller video monitors closer to the operator. The result is an increase of pictures in the operator's immediate eye scan range, but it is inherent in the nature of small video monitors that it becomes more difficult to carefully observe details, such as an individual's face or subtle actions.
The fundamental difficulty is simply the limitation on the area that might be within the comfortable gaze of a single operator. If there are multiple pictures to be monitored, the operator may fail in their assignment because of having to turn their head in the process of trying to observe several large monitors, or simply fail to notice an action if it occurs on one of several small monitors that are located within their immediate gaze.
A different approach to the problem is to utilize a single monitor on which a substantial number of images from different sources (cameras) are displayed. A typical number of images is 16, in a 4.times.4 pattern or array. This can be achieved by performing an image reduction process on each source picture, to turn it into an image of reduced size. Each so reduced image is written into a corresponding area in a buffer memory which stores the total of 16 images, and the buffer memory is scanned as a whole to produce the resulting compound picture of 16 images.
However, although the hardware involved in this approach differs fundamentally from the plurality of monitors discussed above, there are considerable functional similarities. Both approaches generate an array of identical pictures or images of equal area.
One major difference is that with a plurality of separate monitors, the pictures are separated by the physical borders of the various monitor screens, while with a single monitor, the images are generally continuous. The other major difference concerns the size of the system. With a single monitor, the images on it will generally be relatively small even though the monitor will generally be chosen to be relatively large, whereas with a plurality of separate monitors, the pictures will generally be relatively large and placed at a considerable distance from the observer even though the individual monitors may be relatively small.
Such systems therefore generally involve the striking of a compromise between having the system as a whole small enough for all the pictures or images to be readily observable by the observer without inconvenience, and having the individual pictures or images large enough for small details to be readily observable.